1. Field of the Invention
The present invention relates to drive and propulsion systems for ships. In particular, drive and propulsion system having a steering propeller arranged outboard, comprising an azimuth module which can rotate and has a power transmission device, and a propulsion module arranged like a pod on the azimuth module and provided with a drive motor for a propeller.
2. Discussion of the Related Art
A drive technology such as this, which is also known in practice by the expression SSP, is a ship propulsion system which can be rotated, is preferably arranged in the region of the stern of a ship, and at the same time carries out the functions of propulsion, steering and lateral thrust production. The SSP drive is furthermore distinguished by producing little drag on the ship even with the most widely differing ship hull designs, and requires no additional cooling, since this is provided by the water flowing around the drive motor in the propulsion module. Furthermore, the SSP drive has low associated usage and maintenance costs, and offers the advantage of particularly high fuel efficiency.
In the field of ship propulsion technology there is an increasing requirement with regard to the competitiveness of the individual Companies involved to shorten the development times and to reduce the production costs. However, at the same time, propulsion systems are required which can cope with the random failure of one component, so that the maneuverability and controllability of a ship are ensured once again as quickly as possible after a fault occurring in the propulsion system.
Furthermore, it is normal in ship construction for electrical and electromechanical components, such as motors, transformers, switch panels, converter stations, cooling systems or control panels, to be supplied individually by the respective manufacturers to the shipyard, in order then to be installed in the ship by the yard personnel on appropriately provided foundations, and to wired up to one another and for their operation to be tested by the yard personnel. One disadvantage in this case is the considerable logistic complexity and hence considerable cost, which is further increased by the fact that both the manufacture of the individual components and the wiring and testing of the complete system necessitates inspection by a Classification Organization for example the American Bureau of Shipping (ABS), Bureau Veritas (BV), Der Norske Veritas (DNV), Germanischer Lloyd (GL) or Lloyds Register of Shipping (LRS). The present invention is based on the object of providing a drive and propulsion system for ships, which makes it possible to achieve a comparatively high level of safety with regard to reliable maneuverability of a ship, in a comparatively cost-effective manner.
According to the invention, this object is achieved for a drive and propulsion system having the features mentioned above in that at least two steering propellers are provided, whose respective drive motor is in the form of a permanent magnetic synchronous machine, with the stator winding of the synchronous machine having three sections which are connected to a 3-phase alternating current and are connected via the power transmission device to a converter, which is arranged in the ship and is connected on the input side via converter transformers to the ship""s on-board power supply system, and in that a control and regulation device, which comprises standardized assemblies in a modular form, is provided for each of the steering propellers.
A drive and propulsion system designed in such a way takes account, to a major extent, of the increasingly more stringent requirements for the reliability and safety of a ship. This is primarily due to the presence of at least two identical steering propellers with an autonomous control and regulation device, which results in homogeneous redundancy in the propulsion system. When a fault event occurs in a mechanical or electrical component of a steering propeller, there is thus at least one spare drive available, which ensures the maneuverability of the ship.
Since the drive motor is in the form of an electrical synchronous machine, a compact, lightweight construction can be achieved, as is required for arranging the drive motor in the propulsion module. The interconnection of the sections of the stator winding, as well as the converters and converter transformers, result in a three-phase synchronous motor which is operated from the ship""s on-board power supply network, and which makes it possible to achieve an adequate rated rotation speed and a sufficiently high torque at the propeller for the most common ship propulsion system in the power range from 5 W to 30 MW. Furthermore, the modular construction of the control and regulation device, which is composed of standardized modules, contributes to relatively cost-effective production.
In one preferred refinement of the invention, the converter is a network-controlled 12-pulse direct converter, and is connected on its input side to the on-board 3-power supply network via three converter transformers in the form of 3-winding transformers. Firstly, a direct converter can be manufactured cost-effectively and, secondly, it is particularly suitable for operation of large three-phase motors at a low rotation speed, such as those required for ship propulsion systems.
In order to achieve the abovementioned object, the invention furthermore proposes, for a drive and propulsion system of the type mentioned initially, that the drive motor be in the form of a permanent magnet synchronous machine, with the stator winding of the synchronous machine having six sections, of which three are in each case connected to a 3-phase alternating current and, forming a subsystem, are connected via the power transmission device to a converter which is arranged on the ship and is connected on the input side via a converter transformer to the ship""s on-board power supply network, and in that a control and regulation device, which comprises standardized assemblies in a modular form, is provided for each of the two subsystems.
Such a drive and propulsion system also takes account of the random failure of one component and is easy to produce economically, for the reasons mentioned above. The partial redundancy of the drive system resulting from there being only a single steering propeller in this case is achieved by means of the autonomous subsystems, which ensure that at least limited propulsion is maintained for the ship when a defect occurs.
Ship propulsion systems, in particular steering propeller propulsion systems, produce oscillations during operation which propagate through the entire ship""s hull and cause vibration in it. While, in the case of diesel propulsion systems, these oscillations are caused primarily by the reciprocating pistons, it might be supposed that such oscillations would no longer occur in the case of electric motors, such as those used in particular in submarines, but which are also being increasingly used for surface ships. However, this is not the case since, in particular, even a ship""s propeller represents an oscillating load for the propulsion system, to be precise because the propeller blades partly move along the skeg or propeller-shaft stay (which is fitted to the ship""s hull) during their rotational movement but, in contrast, can move largely free from this stay during another part of their rotational movement. This fluctuating load torque is readjusted by the rotation speed regulator, or by the current regulator which is subordinate to it, in order to stabilize the rotation speed of the ship""s screw as exactly as possible at the pre-selected rotation speed nominal value. In this case, the torque (which fluctuates at the shaft rotation speed gas multiplied by the number of blades on the propeller) is transmitted to the drive motor, and is transmitted via its housing to its anchorage, and hence to the ship""s hull. Parts of the ship""s structure are thus caused to oscillate at the fundamental frequency of this pulsating torque and, owing to the mechanical characteristics, the resonance of the ship""s hull is not negligible at the relevant frequency. The vibration resulting from this not only causes stress to the ship""s crew but also results in a considerable load on the entire structure of the ship, and should thus be avoided. The only known way to do this is to calculate the weak points for such oscillations using the so-called finite element method, and to strengthen the critical areas determined in this way by adding additional tons of steel. This method is on the one hand expensive while, on the other hand, it reduces the maximum permissible cargo weight in the ship, increases the fuel consumption and, furthermore, although it may reduce the material-destructive effects of the oscillations produced by the propulsion system, cannot, however, eliminate the cause.
Hydrodynamically speaking, the load on the ship""s propeller is described by its wake field. The fluctuation in this load, which is caused by the skeg or propeller-shaft stay fitted to the ship""s hull, is once again evident in the inhomogeneity of the wake field of the propeller which, in turn, is evident in a fluctuating angle of advance during revolution of the propeller blade. Rotation speed control which keeps the rotation speed of the ship""s propeller stabilized as exactly as possible at the pre-selected rotation speed nominal value has the negative effect that the inhomogeneity of the wake field fully reflects the fluctuation in the angle of advance of the propeller. Any fluctuation in the angle of advance of the propeller reduces the cavitation safety margin of a propeller since, in this case, the operating point of a propeller approaches or exceeds its cavitation limit. Particularly in the region of a skeg or propeller-shaft stay fitted to the ship""s hull, the operating point of the propeller can reach or exceed the cavitation limit, thus initiating cavitation which can then cause considerable damage to the ship and, in particular, to the propeller. Cavitation also leads to unacceptable pressure fluctuations and noise which, in particular, considerably reduces the operational value of passenger, research and military ships.
The disadvantages of the described prior art have resulted in the problem which led to the initiation of the invention of providing a possible way in which the oscillations on the anchorage of a propulsion system, in particular of an entire ship""s hull including the inhomogeneous wake field of a ship""s propeller, which are caused by driving a load at a controlled rotation speed and with a fluctuating torque, in particular in the case of a ship""s propeller, can be reduced as far as possible, or can even be avoided.
In order to solve this problem, the invention provides, for the drive and propulsion system, for the regulation device for damping the oscillations in a drive whose rotation speed is regulated to be only a single rotation speed regulator irrespective of the number of motors operating on one shaft, with the output signal from the rotation speed regulator being fed back to its regulator input. Since the output signal from the rotation speed regulator is approximately proportional to the torque emitted from the drive, then it is possible to achieve a certain amount of insensitivity to torque fluctuations when this output signal is applied, with a suitable phase, to the rotation speed actual value.
It is recommended that the fluctuations in the regulator output signal, which are proportional to the torque, be supplied phase-shifted through approximately 180xc2x0 to the rotation speed regulator input so that, firstly, this results in negative, and hence stable, feedback and, secondly, the torque required to compensate for the load-dependent fluctuations in the rotation speed, and the regulator output signal which is approximately proportional to it, are reduced. In particular, this means that the fluctuations in the drive torque can be reduced considerably, as a result of which the torque fluctuations emitted to the ship""s hull via the anchorage, and the pressure fluctuations transmitted via the ship""s propeller to the ship""s propeller wake field can be reduced to non-critical values. One side effect in this case is that the rotation speed of the propeller does not remain exactly constant, but is subject to certain fluctuations, caused by the changing load. However, this is of very minor importance for the forward propulsion produced by the propeller. On the other hand, this advantageously allows the moment of inertia of the rotor of the electric motor, of the propeller and of the shaft to be used to damp these oscillations. Since the shaft is mounted such that it rotates with a virtually no friction, the ship""s hull is not excited by these rotation speed fluctuations.
Speaking hydromechanically, this effect has the major advantage that the rotation speed of the propeller does not remain exactly constant, but is subject to certain fluctuations which are caused by the changing loads on the propeller; this reduces the fluctuation width caused by the hydromechanically coupling between the wake field and the angle of advance. This reduction in the fluctuation width of the angle of advance results from the fact that the fluctuation in the load on the propeller blade located in the inhomogeneous wake field of the skeg or propeller-shaft stay fitted to the ship""s hull leads, owing to the above effect of the invention, to a change in the rotation speed whose direction and magnitude counteract its cause, thus leading to damping of the fluctuation width of the angle of advance of that propeller blade which is most at risk of cavitation. The reaction of this propeller blade on the other blades of the propeller resulting from the described effect is of minor importance, since their operating points remain considerably closer to the rated operating point of the propeller than the operating point of that propeller blade which is located in the inhomogeneous wake field of the skeg or propeller-shaft stay which is fitted to the ship""s hull.
It is within the scope of the present invention for the output signal fed back from the rotation speed regulator to be multiplied by a factor. This feedback should, of course, be chosen such that it is not too strong, since, otherwise, the approximately constant mean value of the drive torque, which is likewise fed back, would result in major reduction in the rotation speed nominal value, and on implementation of the rotation speed regulator, having a PI characteristic, would itself no longer be able to accelerate the propulsion shaft to the selected rotation speed nominal value. Since, on the other hand, a predetermined voltage range, for examplexe2x88x9210 V to +10 V, is available both for the regulator input signal and for its output signal, in which case the limit values respectively correspond to the maximum rotation speed for traveling ahead and traveling astern, or to the maximum motor torque, multiplicative matching of these two signal levels is essential for selecting an optimum amount of feedback.
A development of this idea of the invention provides for the multiplication factor to be between 0.01% and 3%, preferably between 0.1% and 2.0%, and, in particular, between 0.15% and 1.5%. This is intrinsically a very low level of feedback sincexe2x80x94as already mentioned abovexe2x80x94the majority of the power required by the alternating load can be taken from the moment of inertia of the rotor of the electric motor, of the propeller and of the propulsion shaft, and can in each case be fed back to them once again. Since the invention provides a certain degree of freedom for rotation speed fluctuations in this case, the propulsion train can advantageously be used as an energy store which, in a similar way to the energy-storage capacitor in an electrical power supply, contributes to the smoothing of the power consumption from the electrical supply network for the propulsion system. A small amount of feedback here therefore leads to the noteworthy result that the torque to be applied by the drive motor is largely smoothed, without this causing any significant, permanent control error from the pre-selected nominal value.
With regard to the design selection of the level of feedback according to the invention, such a setting has been proven at which the steady-state control error is between approximately 0.2% and 1.5% at the rated load. In a case such as this, despite the negative feedback of the regulator output signal, the quality of the control system, in particular the dynamic response to changes in the rotation speed nominal value, is not adversely affected.
The invention also provides for the steady-state control error to be compensated for by a corrected nominal value. Since the steady-state control error in the control loop structure according to the invention is calculable, then it can be largely compensated for by means of a correction circuit.
One compensation method that is preferred by the invention uses the estimated, mean load on the drive as an output variable and attempts, by mathematical calculation of the control system parameters from this, to determine the steady-state control error to be expected, and to compensate for this by means of appropriate adjustment of the rotation speed nominal value in the opposite sense.
In the case of propeller propulsion systems for ships, the control system has at least approximately known characteristics, and in particular, the steady-state mean load torque is obtained from the steady-state rotation speed actual value in accordance with a characteristic. For propeller propulsion systems, the drive torque in this case rises approximately with the square of the rotation speed actual value. Thus, if the rotation speed actual value is intended to correspond to a specific WCSA rotation speed nominal value, then it is possible to use this characteristic to approximately determine the torque which is approximately proportional to the regulator output signal in the steady state, so that the mean value of the fed back signal, and hence the residual control error, can also be determined. Since, in a case such as this, this is added to the (ideal) nominal value, preferably additively, then the ideal rotation speed nominal value actually corresponds precisely with the occurrence of the already calculated control error as the rotation speed actual value.
In accordance with the idea of the present invention, the rotation speed regulator may have a PI characteristic. In the steady state, this results in the steady-state rotation speed actual value being extremely stable, and largely matching the ideal rotation speed nominal value thanks to the prior distortion according to the invention.
Although the control system according to the invention can be used for virtually all propulsion shafts with approximately cyclically fluctuating load torques, one very particularly important, and hence preferred field of use, is the control of an electrical propeller propulsion system for surface ship or submarines. In particular, in conjunction with the drive and propulsion system according to the present invention, since the characteristics of the propeller result in severe torque fluctuations and, secondly, the cyclic variations in the drive torque to be applied by a motor for stabilization cannot actually, in the case of ships, be introduced into an anchorage component which is immovably fixed on a base, since they are invariably introduced into the moving ship""s hull.
The output from the rotation speed regulator of corresponding control devices for drive and propulsion systems is the nominal value of a current regulator for the converter and must not vary more rapidly than the on-board power supply network for the propulsion device for the ship""s propeller can follow dynamically. The dynamic limits for load changes in the on-board power supply network depend on diesel generators in the diesel generator system. In this case, the diesel engine and the generator in the diesel generator system, which is normally in the form of a synchronous generator, can be considered separately from one another. When designing the load response of diesel engines for diesel generator systems in ships, it is necessary to comply with the requirements of the International Association of Classification Societies (IACS). The three-stage load change diagram described there has a considerable effect, with present-day highly boosted diesel engines, on the dynamic response of the drive and propulsion system for ships propellers, in particular steering propellers. A further exasperating factor is that the values quoted there are often no longer satisfied these days, owing to lack of adequate maintenance, particularly in the upper power region. The feasible dynamic response for the power output on the diesel engine shaft therefore decreases, from experience, when the ship has been at sea for a lengthy time.
A further time gradient of the power output from diesel engines, which is not specified in a generally applicable manner by IACS or elsewhere, depends on the thermal load capacity of the diesel engines. A uniform load change on a warmed-up diesel engine from 0% to 100% rated power or from 100% rated power to 0% must be carried out in only a minimum time which is highly dependent on the physical size of the respective diesel engine. This time gradient must not be exceeded, even in places, since otherwise, the diesel engine may be damaged. These minimum times explained above may be between 10 seconds for small sizes, and 60 seconds for large sizes.
Converters with a control wattless component, for example current intermediate circuit converters, direct converters, converters for DC machines and the like, require a load-dependent wattless component. This wattless component is supplied by the field for the synchronous generators in the diesel generator system. The time gradient of the load-dependent wattless component from the converters mentioned above with a control wattless component is approximately 15 to 25 times faster for propulsion devices for ship""s propellers than can be followed by the field of the synchronous generators in the diesel generator system.
If the propulsion system for ship""s propellers exceed the dynamic limits of the diesel engines in the diesel generator system, the frequency of the on-board power supply network supplied by the diesel generator system fluctuates to unacceptable extents. It is also possible for the diesel engines to be damaged, since the rotation speed control for the diesel generator system must keep the frequency of the on-board power supply network within a permissible range irrespective of the dynamic limits. If the dynamic limits of the synchronous generators in the diesel generator system are exceeded, the voltage of the on-board power supply network fluctuates unacceptably.
Thus in the past, test journeys were carried out experimentally based on varying run-up times for the rotation speed nominal value and/or on current nominal value in a number of steps or continuously until the propulsion device for the ship""s propeller could be operated satisfactorily in the on-board power supply network that was supplied with electrical power by the diesel generator system. In this case, it was often only possible to optimize specific operating points. There was no fixed relationship between the adjustment capabilities in the control system for the electrical propeller motor and their dynamic effects on the diesel generator system in the on-board power supply network. The time profile for reducing the load on the diesel generator system was rarely taken into account, or adjustable, in the control system for the propulsion device for the ship""s propeller.
For the purposes of the present invention, a diesel engine is used to represent internal combustion engines as a drive motor for a synchronous generator. However, internal combustion engines may also be used which are operated using diesel, marine diesel, heavy oil etc., and steam turbines or gas turbines may also be used as drive engines. If the drive engine is a steam turbine or gas turbine, the IACS load change diagrams are inapplicable, and the time gradient of the load output is in a different range, which means that times which differ from those quoted are applicable to the run-up and run-down times of the adaptive ramp transmitter for the current nominal value of the current regulator.
If the run-up and run-down times for the adaptive ramp transmitter for the current nominal value of the current regulator can be varied in proportion to the magnitude of the actual rotation speed of the electric propeller motor, this ensures that the run-up and run-down times for the ramp transmitter for the current nominal value are based on the maximum permissible rate at which the diesel engines in the diesel generator system which supply the on-board power supply network with electrical power can have loads applied to them and removed from them. This means that the real power consumed by a converter associated with the drive device for the ship propeller has a run-up and run-down time which is independent of the rotation speed of the electrical propeller motor.
A minimum run-up and a minimum run-down time are preferably predetermined for the run-up time and the run-down time of the adaptive ramp transmitter for the current nominal value of the current regulator in a lower rotation speed range of the electric propeller motor or of the ship""s propeller, which are dependent on the maximum permissible rate of change of the wattless component emitted by synchronous generators in the diesel generator system which feeds the on-board power supply network.
If the run-up and run-down times of the adaptive ramp transmitter for the current nominal value of the current regulator can be changed in inverse proportion to the number of diesel generators in the diesel generator system which supply electrical power to the on-board power supply network, this means that the real power consumed from a diesel generator in the diesel generator system has a run-up and run-down time which is independent of the operation of the converter associated with the drive device for the ship""s propeller.
In one expedient refinement of the drive device for ship""s propellers according to the invention, the run-up and run-down times of the adaptive ramp transmitter for the current nominal value of the current regulator can be varied as a function of the operating state of the diesel generator system which supplies electrical power to the on-board power supply network, in which case different diesel generators in the diesel generator system may be used in different operating states.
If the output value from the rotation speed regulator corresponding to the nominal rotation speed can be entered both directly in the current regulator of the converter for the electric propeller motor and in the adaptive ramp transmitter, whose output value can be entered via a positive offset step in an upper current value limiting unit for the rotation speed regulator and, via a negative offset step, into a lower current value limiting unit for the rotation speed regulator, this means that the rotation speed regulator can control the current nominal value to be passed onto the current regulator without any limits when it is in the stabilized state. Otherwise, considerable beat frequencies would occur in the electric propeller motor, and these would appear as mechanical oscillations or structure-borne sound sources in the ship, in particular, there would be a risk of the ship""s propeller starting to cavitate, which in turn could lead to damage to the ship""s propeller and to the ship. In the procedure described above, the output of the adaptive ramp transmitter maps the maximum permissible dynamic response of the diesel generators explained and described above. The positive and negative offset steps of the adaptive ramp transmitter and the upper and the lower current value limiting units for the rotation speed regulator are used to provide the required rotation speed control freedom. It is thus possible for the rotation speed regulator to control the current nominal value, which is to be passed on to the current regulator for the converter, via a xe2x80x9cmoving windowxe2x80x9d, within which the rotation speed regulator is free in terms of rotation speed control.
Within this moving window, the rotation speed regulator operates with its full dynamic range. This thus leads to voltage fluctuations in the on-board power supply network, since the excitation for the synchronous generators in the diesel generator system can no longer follow the rate of change of the current nominal value. The reactive current on the on-board power supply network side from the converter for the drive device for the ship""s propeller produces these voltages fluctuations via the reactance of the generator. The magnitude of the offset in the positive offset step and negative offset step, and hence the variation width and the magnitude of the moving window are set such that any on-board power supply network side reactive current resulting therefrom produces, across the reactance of a synchronous generator in the diesel generator system, a voltage drop which is within the maximum permissible voltage tolerance of the on-board power supply network. In consequence, no disturbances occur, since rapid voltage fluctuations within the maximum permissible voltage tolerance are not critical in the on-board power supply network. In this case, the magnitude of the offset is a function of the rotation speed, with the on-board power supply network side power factor being dependent on the drive level of the converter associated with the drive device for the ship""s propeller.
The magnitude of the offset is proportional to the number of diesel generators which are feeding electrical power to the on-board power supply network, since the short-circuit rating Skxe2x80x3 in the on-board power supply network is likewise approximately proportional to the number of diesel generators producing the supply.
When the actual rotation speeds of the ship""s propeller or of the electrical propeller motor rise, their dynamic response changes considerably. The dynamic response of the ship""s propeller decreases more than proportionally as the actual rotation speeds rise, on the basis of the family of propeller curves (towing curves-free drive curve).
In the case of drive and propulsion systems for ships that are known from the prior art, the regulation device comprises a rotation speed regulator with which the electric propeller motor is associated and whose output signal, the torque nominal value or current nominal value, regulates the rotation speed of the electric propeller motor via a converter, and a ramp transmitter, in which a rotation speed nominal value for the electric propeller motor can be entered and by means of which a rotation speed nominal value profile can be preset for the rotation speed regulator, by means of which the actual rotation speed of the electric propeller motor can be matched to the rotation speed nominal value for the electric propeller motor as entered in the ramp transmitter. In this case, the run-up time preset by the ramp transmitter by means of the nominal value preset, is increased in one to three steps as the rotation speed of the electric propeller motor rises, in order to match the drive device to the ship""s propeller curve.
This conventional configuration of the matching of the drive device to the ship""s propeller curve has considerable disadvantages. Starting from a rotation speed of 0, the electric propeller motor in the drive and propulsion system initially accelerates optimally. The power of the electric propeller motor then rises ever faster during a run-up process with a constant run-up time, until a current limit on the output side of the rotation speed regulator allows the power to be increased further only at a low rate.
If the run-up time is then switched during the transition from one stage to the next stage, the acceleration power provided by the electric propeller motor in the drive and propulsion system decreases to approximately 0. The power from the electric propeller motor in the drive and propulsion system now in this stage rises again during the further run-up with a constant run-up time, although this is now longer, as described above. In this way, the electric propeller motor in the drive and propulsion system pumps the power required for acceleration of the ship""s propeller out of the ship""s on-board power supply network. This has the unpleasant effect for ship control that the drive and propulsion system drops into a hole when accelerating over certain rotation speed ranges, and effectively stops. Furthermore, the power demand pumped by the drive and propulsion system from the ship""s on-board power supply network is therefore also undesirable, since it necessitates an unnecessary power margin in the on-board power supply network.
The current limit for the electric propeller motor in the drive and propulsion system for ships propellers of this generic type and as described above occurs, when calculated roughly, at about ⅓ of the rated torque over the respective ship""s propeller curve. The range between the current limit for the electric propeller motor and the calculated ship""s propeller curve is required to ensure that there is also a margin for heavy seas and/or ship maneuvering in addition to the acceleration torques required for ship acceleration processes. The ramp transmitters used in the past for drive devices for ship""s propellers which were controlled in steps are unable to assign a defined acceleration torque to the electric propeller motor during acceleration processes and, in fact, they simply produce only the respective current limits appropriate at that time over wide rotation speed ranges of the electric propeller motor. This is because the ship""s acceleration time is several times the run-up time for this type of ramp transmitter.
The invention is thus also based on the object of developing the drive and propulsion system for ships mentioned initially such that the ship propeller can be accelerated more uniformly by means of the electric propeller motor for the drive device, without any current limit. Furthermore, the configuration according to the invention is intended to ensure that the power required for acceleration processes for the ship""s propeller is produced at the respectively desired level by the electric propeller motor, with the aim being to reduce or avoid unnecessary spare power capacities in the ship""s on-board power supply network.
According to the invention, this object is achieved by the ramp transmitter being in the form of an adaptive ramp transmitter and having a characteristic transmitter which can be controlled by the magnitude of the rotation speed actual value of the electric propeller motor. The adaptive ramp transmitter and its characteristic transmitter provide the capability for the drive and propulsion system according to the invention for ships to produce a definable acceleration torque in addition to a steady-state load torque for the electric propeller motor. Particularly when the actual rotation speeds of the electric propeller motor are relatively high, this definable acceleration torque can to a certain extent be kept constant, which means that no unnecessary high acceleration torque values occur, even at times. Interaction with active oscillation damping, which is not described here, and readjustment of the ramp transmitter also allows, inter-alia, the tendency of a ship""s propeller to cavitate or to produce bubbles to be reduced or suppressed. This applies even during extreme ship maneuvers.
In order to match the adaptive response of the drive and propulsion system according to the invention to the operator characteristics of the electric propeller motor and of the ship""s propeller, it is advantageous to be able to preset different dependency levels between the actual rotation speed of the electric propeller motor and the run-up time in the characteristic transmitter of the adaptive ramp transmitter for different actual rotation speed ranges of the electric propeller motor.
In order to make it possible to optimize the drive and propulsion system according to the present invention for ships in terms of the various target functions, for example minimum fuel consumption, minimum time passing, high maneuvering capability for the ship etc., it is advantageous to set the dependency level between the actual rotation speed of the electric propeller motor and the run-up time preferably continuously, at least when the electric propeller motor is operating in a relatively high actual rotation speed range.
In order to ensure that the electric propeller motor, and hence the ship""s propeller, can operate in a maneuvering range with a wide dynamic range, defined comparatively low actual rotation speeds, it is advantageous if it is possible to preset a constant, short run-up time in the characteristic transmitter of the adaptive ramp transmitter when the electric propeller motor is in a low actual rotation speed range, for example between 0 and ⅓ of the rated rotation speed.
In order to ensure uniform acceleration of the ship""s propeller, largely free of any current limit, by the electric propeller motor in a comparatively high actual rotation speed range, it is expedient to be able to preset a run-up time which rises sharply as the actual rotation speed of the electric propeller motor rises in the characteristic transmitter of the adaptive ramp transmitter when the electric propeller motor is in a high rotation speed range, for example between xc2xd of the rated rotation speed and the rated rotation speed. The characteristic transmitter thus effectively then associates a run-up time with each rotation speed actual value in this relatively high actual rotation speed range.
In order to ensure that the drive and propulsion system according to the invention makes a smooth transition between the comparatively low actual rotation speed range and the comparatively high actual rotation speed range of the electric propeller motor, it is advantageous to be able to preset a run-up time which rises less sharply than the high actual rotation speed range, as the actual rotation speed of the electric propeller motor rises, in the characteristic transmitter of the adaptive ramp transmitter for a medium actual rotation speed range of the electric propeller motor which is between the low and the high actual rotation speed ranges, for example between ⅓ of the rated rotation speed and xc2xd of the rated rotation speed.
During normal operation of the ship, a characteristic which is stored in the characteristic transmitter is used which has been deliberately selected as a compromise between adequate ship maneuvering characteristics and a method of operation which protects the entire machine system. In order to increase the maneuverability of the ship to a major extent in an emergency, it is advantageous for the adaptive ramp transmitter to be connected to an input unit, by means of which the run-up times predetermined in the characteristic transmitter can be set to minimum values, excluding any consideration of technically dependent limit values.
According to one advantageous development of the present invention, each one of several converters is connected to a network-controlled 6-pulse direct converter and, on its input side, is connected to the on-board power supply network via a converter transformer in the form of a 4-winding transformer. If the primary windings of the two converter transformers are in this case expediently arranged offset through 30xc2x0 with respect to one another, this results in the two subsystems having a 12-pulse network reaction on the ship""s on-board power supply network.
It is particularly advantageous if both subsystems can be operated in parallel, in which case one of the regulation and control devices of the subsystems can be used as the master, and the other can be used as a slave. Parallel operation of the two subsystems firstly results in active redundancy in the propulsion system while, secondly, the master-slave arrangement of the regulation and control devices ensures higher-level control of both subsystems. This makes it possible for certain tasks, such as rotation speed regulation, to be carried out exclusively by the regulation and control device that is used as the master, and for it to be impossible for these tasks to be carried out by that which is used as a slave.
It is furthermore advantageous for each subsystem to have an associated programmable safety device which, in addition to alarm signals, also produces regulation and control signals automatically. Such regulation and control signals make it possible, for example, to reduce the motor rotation speed or the stator current without any delay when a defect is detected in one of the subsystems.
According to a further feature of the invention, each converter has phase current regulation. This offers the advantage that the current at a variable frequency can be applied to the synchronous machine. According to a further feature of the invention, the phase current regulation is preceded by field-oriented regulation in the form of transvector control, in order to give the propulsion system a good dynamic response. The object of the transvector control in this case is to determine the orientation of the magnetic flux from the actual values of the stator voltage, stator currents and rotor position of the synchronous machine, with the nominal value of the torque-forming stator current being preset at right angles to the flux axis that is determined.
One development of the present invention furthermore provides a monitoring device, by which the power generation and distribution in an on-board power supply network can be protected against being overloaded by the drive motor. This ensures that the nominal value of the rotation speed is restricted when the propeller power required by the predetermined nominal value exceeds the available electrical power in the ship""s on-board power supply network. Furthermore, in the event of defects in the on-board power supply network, it is possible to preset a different nominal value, in order to avoid overloading of the power generation equipment, and hence a xe2x80x9cblackoutxe2x80x9d in the on-board power supply network.
According to a further preferred refinement of the invention, the individual components of the drive and propulsion system are arranged in at least one prefabricated container. In this context, the term container means a virtually autonomous functional unit which is provided with interfaces to other ship systems, for example the control system. This offers the capability to connect the propulsion system, and to check its operation, largely independently of its location in the ship. After being dispatched to the shipyard, all that is then necessary is to mount the container on a predetermined foundation in the ship, and to connect it to its power and control system. Since there is thus no need to connect the individual components of the propulsion system in the shipyard, there is no need either for logistic support for the individual components in the shipyard, thus resulting in simpler and clearer logistic planning. Furthermore, this allows flexible delivery and hence installation of the container to be achieved at an optimum time. The use of a single foundation for the container rather than separate foundations for the individual components also ensures that the manufacturing complexity is reduced, and is hence more cost-effective.
In order to allow a prefabricated container to be transported to the shipyard using conventional container ships, the present invention provides that the dimensions of the containers be standardized.
According to a further advantageous proposal of the present invention, a unit for remote position monitoring is arranged on the container. This may preferably be a GPS system. This makes it possible to use the GPS system to determine the exact location of a container. It is thus possible to check the movement of the container from the loading point via the transport to the destination. Existing GPS systems, for example, can be used for this purpose, for example the IN MAR SAT system which is already used for maritime purposes. This refinement makes it possible in a simple manner to ensure that the corresponding containers are sent by the correct route to the correct destination. This configuration of the GPS units as removable units on the container, for example units comprising a transmitter, power supply and the like, allows the unit to be removed from the container, and to be reused, once the container has arrived at the correct location.
The invention is furthermore based on the object of developing the initially mentioned drive and propulsion system such that the electric propeller motor can be accelerated, decelerated or electrically braked without any risk of problems, caused by fast load changes, in the on-board power supply network or in the area of the diesel generator system.
According to the present invention, this object is achieved by an adaptive ramp transmitter, by which time matching of the current nominal value of a current regulator of the converter to the current nominal value corresponding to the nominal rotation speed present at the rotation speed regulator, can be controlled. This takes into account limit values predetermined by the on-board power supply network and/or by the diesel generator system which feeds the on-board power supply network with electrical power.